The present invention relates to the field of video signal processing associated with television signals and the like, and more particularly to a method and apparatus for canceling jitter in a video signal.
Conventionally, when a video signal processing apparatus, for example, a waveform display device such as a waveform monitor, receives an input video signal (or television signal) for displaying its waveform, the apparatus may use a synchronization signal received from the outside, which is different from a synchronization signal extracted from the received video signal. For example, in a studio involved in the production of television programs, a single reference signal is provided for synchronizing multiple video signal programs used in the studio with one another, such that the multiple video signal programs are synchronized with the reference signal. Conventionally, a technique has been known for generating a synchronization signal (or a trigger signal) for video signals from such an external reference signal (see, for example, Laid-open Japanese Patent Application No. 11-215447). A trigger generator circuit based on the technique described in Laid-open Japanese Patent Application No. 11-215447 employs either a PLL circuit for locking the phase to a vertical synchronization signal or a counter started by the vertical synchronization signal for generating a trigger signal, such that the trigger signal is generated at a horizontal scanning line period associated with the video signal type of a received video signal (interlace or non-interlace SDTV (Standard Definition Television signal) or HDTV (High Definition Television Signal)).
In the waveform display device employing the trigger generator circuit as described above, however, when an external trigger signal generated from the outside is switched to an internal trigger signal internally generated from an input video signal, and vice versa, a video signal can experience jitter in a frame period or a horizontal scanning line period.